I've had to make some top lever springs for Syracuse Lefevers. That seems to be a relatively common malady with them. Gun parts dealers seldom have them because they get bought quickly by guys who need one. My theory is that possibly the company either made or purchased a fairly large quantity of them that were either hardened and drawn incorrectly, or they used a type of steel that wasn't suitable for the job. I've never had a broken Lefever hammer spring, so my theory about the top lever springs seems plausible.
In every one that I've encountered, the broken peices were present inside the gun when I disassembled it.. So it was a pretty simple matter to match the two broken pieces to get the correct dimensions to make a replacement. There is a great deal of information on the internet, and in the atchives here, on how to make a simple vee spring. But as with all gun repairs, people who don't have the proper tools, knowledge, materials, and patience to do a job without causing further damage will be money ahead to pay a professional.